EFFECT OF CRUDE OIL POLLUTION ON OYSTERS 
149 
muscle attachment. There was no evidence of a mortality of these natural enemies 
or of impairment of tlieir growth and reproduction on many areas where a high per- 
centage of the oysters had died previously. 
9. A small percentage of the dead oysters and those in a weakened and dying 
condition showed no serious shell injury by the boring sponge and boring clam. 
There was one case in particular at station 6 where 95 percent of the oysters had 
died on a temporary storage bed and were free of shell infestations of these organisms. 
This bed is located approximately 5}i miles south of the Barre wells. 
10. The field studies at the 27 stations in Terrebonne Parish failed to disclose 
any direct evidence of the destruction of marine animals or plants by oil-well pollution. 
As indicated previously, conditions throughout tins region and in the immediate 
vicinity of the oil wells were found to be decidedly favorable for reproduction of adult 
oysters and for the development, attachment, and growth of oyster larvae and spat. 
Several other mollusks such as the boring clam, shipworm, mussel, Crepidula, Anomia, 
and the common borer showed no evidence of unusual mortality and were found to 
be reproducing and growing throughout this region in an apparently normal manner. 
Barnacles and green algae were abundant on the piling of the oil wells and were 
thriving on submerged cross beams at the Barre well at a distance of 5 feet from the 
bleed- water discharge where they were subjected continually to a mixture of this 
effluent and sea water. Blue crabs were observed feeding on these forms at the 
latter location during the period that the effluent and oyster samples were being 
collected. 
Many species of fish such as trout, croaker, alligator gar, bonnet head shark, 
channel bass, and bluefish were caught or observed at the Pelto well within 100 feet 
of the bleed-water discharge. At the Barre well many schools of immature fish, 
measuring from approximately one-half inch to 3 inches were actively swimming and 
feeding at distances ranging from 3 to 25 feet from the effluent discharge. 
11. Hydrographical observations . — Determinations of water temperature, specific 
gravity, and hydrogen-ion concentration were made at all stations during the period, 
May 23 to June 1. The records of water temperature give an average of 28.1° C. 
(86.6° F.) and range from 27° to 29° C. 
Measurements of specific gravity at surface and bottom, corrected to 17.5° C., 
range from 1.0118 to 1.0174 with an average figure of 1.0143. When converted into 
terms of salinity (grams of salt per 1,000 grams of sea water) the concentration of 
salts shows a variation of 15.41 to 22.77 per mille, with an average of 18.69 per mille. 
These salinities are favorable for oyster growth and reproduction and correspond to 
those found on some of the best oyster-producing areas in this country. The present 
records of specific gravity have been compared with those obtained in 1906 and 1907 
by the United States Bureau of Fisheries (Moore and Pope, 1910) and the Gulf 
Biologic Station (Cary, 1907) and show that the salt content of the water in Terre- 
bonne Parish was essentially the same in 1933 as at that time. 
The observations of hydrogen-ion concentration (as expressed in pH) show an 
average pH of 8.3 and range from 8.2 to 8.6. These also compare favorably with the 
Bureau’s records of this factor in other oyster-producing regions. Water samples, 
collected in the immediate vicinity of the Barre and Pelto wells (100 and 300 feet from 
brine discharge pipes) showed no appreciable difference in liydrogen-ion concentration 
and salinity at surface and bottom, and no noticeable increase in these factors as com- 
pared with conditions on the various oyster beds. 
143870—35 2 
